The ceramic particles increase a hardness of the precious metal matrix composite compared to the continuous metal material without the ceramic materials. The pr

The ceramic particles increase a hardness of the precious metal matrix composite compared to the continuous metal material without the ceramic materials. The precious metal matrix composite includes about 75% precious metal by mass. Ok, that makes more sense. The ceramic would indeed make the resulting composite harder. And has a side benefit of reducing the amount of gold used. Starting from 24k (pure) gold, the 75% ratio gets them to 18k, commonly used in jewelry in the US.